This paper examines the career of Charles Macklin of London, an 18th-century actor/director/teacher, whose treatise on his performative approach and pedagogical techniques, "On the Science of Acting," was lost at sea in a 1772 shipwreck. Citing two letters Macklin received from his actress daughter, Maria, and fragments of his own accounts as well as contemporary comments, the paper considers what might have been included in his lost treatise. The first part discusses Macklin's acting--he was on the stage for nearly 70 years and is credited with anticipating Garrick in developing a more natural acting style. According to the paper, his portrayal of Shylock in "The Merchant of Venice" was probably his best role; Alexander Pope is known to have exclaimed: "This is the Jew that Shakespeare drew." The second part discusses Macklin's pedagogy, noting that at every stage of his career he taught acting. The paper quotes remarks from his students which confirm that his teaching was like his personality--kindly but "no nonsense." It states that Macklin began by ridding his students of all formality and artificiality of manner, and when he felt the student was able to achieve a "naturalism" in his delivery, then Macklin had the performer "accommodate techniques to the requirements of the play." The paper also examines Macklin as a director. It concludes that, through personal example and his students, Charles Macklin had a pervasive influence on the mid-18th century trend toward a more natural acting style. Contains a picture of Macklin and a 22-item bibliography. (NKA)